1. Field of the Invention
The present invention relates to a resist material and an exposure method which are used in microfabrication in, for example, the field of semiconductor.
2. Description of Related Art
In, for example, the field of semiconductor, as the degree of integration of semiconductor devices is increasing, an urgent task is to establish a new processing technique which enables processing of an ultra-fine pattern as small as, for example, 0.1 μm or less.
A so-called lithography technique is indispensable to processing of a fine pattern. For improving the optical resolution in the lithography technique by using a light for exposure having a shorter wavelength to apply the lithography technique to ultra-fine processing, the conventional lithography technique using a g-line or i-line from a mercury lamp or an ultraviolet light from a KrF (krypton-fluorine; wavelength: 248 nm) or ArF (argon-fluorine; wavelength: 193 nm) excimer laser has been applied to commercial use. These techniques have a restriction of resolution due to the wavelength of the used light so that they are applied to the devices according to the design rule of 0.13 μm or more.
On the other hand, another urgent task is to develop a new lithography technique which enables fabrication of devices according to the design rule 0.1 μm or less. Therefore, vigorous studies are being made on development of a new exposure technique using a vacuum ultraviolet (hereinafter, frequently referred to simply as “VUV”) light having a wavelength of 170 nm or less, which is even shorter than the wavelength of a light source for exposure used in conventional lithography techniques. Specifically, as a substitute for ArF lithography which is a current lithography technique, a lithography technique using a F2 (fluoride dimer) excimer laser (wavelength: 157 nm) as a light source is being developed. Further, a substitute for F2 lithography, a lithography technique using an Ar2 (argon dimer) excimer laser (wavelength: 126 nm) as a light source is proposed.
However, a general organic material conventionally used as a resist material in lithography has a problem in that it exhibits high optical absorption in the wavelength range of a VUV light, and thus the light radiated does not reach the bottom portion of the resist layer, so that a preferable rectangular resist pattern cannot be formed, causing deterioration of the resist pattern. Specifically, for example, a resin which is a main skeleton of the polymer constituting the resist material generally used, such as a novolak resin (for i-line lithography), a polyhydroxystyrene resin (for KrF lithography), or an acrylic resin (for ArF lithography), has a high optical absorption in the wavelength range of a VUV light. Therefore, these resins cannot be used as a resist material for VUV lithography.
In order to solve the problem of the resist pattern deterioration, a method has conventionally been employed in which thickness of a resist is reduced to about 70 nm or less to improve a collective transmittance of the resist layer. However this method poses problems in that the resist layer cannot exhibit a satisfactory etching resistance due to the small thickness of the resist, and that the small thickness of the resist causes the number of defects in the resist layer to increase.
Further, in order to solve the problem of the resist pattern deterioration, another method has been used. Specifically, there has been used a surface-imaging method utilizing silylation which enables formation of a pattern in the resist layer even when the resist layer has a low transmittance. However, the surface-imaging method has problems in that the resist pattern suffers an edge roughness, and that the dimensional control property is unsatisfactory.